Observations and Modelling of Fronts and Frontogenesis

dominates the spectrum. At these wavenumbers and at
wavenumbers above 1 cpkm, the spectrum is approximately
constant. Between 0.1 cpkm and 1 cpkm, the spectrum is very
nearly proportional to k1-, where k is wavenumber.
We associate the low wavenumber plateau with the
mesoscale eddy field, the likely source of the dominant
temperature features. The constant spectral level is a
typical signature of an eddy production range, which may be
driven by baroclinic instability. This instability generally
prefers the scale of the internal deformation radius. The
first local internal deformation radius, calculated using a
FRONTS 80 CTD station for the upper 1500 m supplemented by
deep data from a 1984 meridional transect, is 40 km, which
lies within the energetic plateau, toward its less resolved
low wavenumber end. The break in slope at the high
wavenumber end of the plateau occurs near 0.1 cpkm, at
roughly the fifth internal deformation radius. The constant
spectral level at wavenumbers above 1 cpkm is likely due to
temperature gradient production in the surface boundary
layer.
Figure 11.9 displays horizontal wavenumber spectra of 15
m horizontal temperature gradient from each individual tow,
band averaged to 10 bands per decade. The spectral levels
vary by roughly half a decade. The spectral shapes are
nearly uniform, despite the apparent difference in the
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